Role of estrogen in balancing contributions from multiple memory systems

In addition to modulating memory per se, estrogen alters the learning strategy used to solve a task, thereby regulating the quality of information processed by the brain. This review discusses estrogen's actions on cognition within a memory systems framework, highlighting our work with a variety of paradigms showing that learning strategy is sensitive to estrogen even when learning rate is not. Specifically, high levels of gonadal steroids, in particular, elevations in estrogen, bias female rats toward using hippocampal-sensitive approaches while low levels of gonadal steroids promote the use of non-hippocampal sensitive strategies. In light of findings from a variety of approaches involving the hippocampus in allocentric and the striatum in egocentric response patterns, it is likely that estrogen alters the relative participation of these, and most undoubtedly other, neural systems during cognition. Changes in neuromodulators such as acetylcholine that regulate other processes such as inhibitory tone and excitability reflect one mechanism by which estrogen may orchestrate learning and memory. (C) 2004 Elsevier Inc. All rights reserved.